Humanities › History & Culture Gadsden Purchase Share Flipboard Email Print Getty Images History & Culture American History Basics Important Historical Figures Key Events U.S. Presidents Native American History American Revolution America Moves Westward The Gilded Age Crimes & Disasters The Most Important Inventions of the Industrial Revolution African American History African History Ancient History and Culture Asian History European History Genealogy Inventions Latin American History Medieval & Renaissance History Military History The 20th Century Women's History View More By Robert McNamara History Expert Robert J. McNamara is a history expert and former magazine journalist. He was Amazon.com's first-ever history editor and has bylines in New York, the Chicago Tribune, and other national outlets. our editorial process Robert McNamara Updated February 02, 2019 The Gadsden Purchase was a strip of territory the United States purchased from Mexico following negotiations in 1853. The land was purchased because it was considered to be a good route for a railroad across the Southwest to California. The land comprising the Gadsden Purchase is in southern Arizona and the southwestern part of New Mexico. The Gadsden Purchase represented the last parcel of land acquired by the United States to complete the 48 mainland states. The transaction with Mexico was controversial, and it intensified the simmering conflict over slavery and helped to inflame the regional differences that eventually led to the Civil War. Background of the Gadsden Purchase Following the Mexican War, the boundary between Mexico and the United States set by the 1848 Treaty of Guadalupe Hidalgo ran along the Gila River. Land to the south of the river would be Mexican territory. When Franklin Pierce became president of the United States in 1853, he backed the idea of a railroad that would run from the American South to the West Coast. And it became apparent that the best route for such a railroad would run through northern Mexico. The land to the north of the Gila River, in United States territory, was too mountainous. President Pierce instructed the American minister to Mexico, James Gadsden, to purchase as much territory in northern Mexico as possible. Pierce's secretary of war, Jefferson Davis, who would later be the president of the Confederate States of America, was a strong supporter of a southern rail route to the West Coast. Gadsden, who had worked as a railroad executive in South Carolina, was encouraged to spend up to $50 million to buy as much as 250,000 square miles. Senators from the North suspected that Pierce and his allies had motives beyond simply building a railroad. There were suspicions that the real reason for the land purchase was to add territory in which slavery could be legal. Consequences of the Gadsden Purchase Because of objections of suspicious northern legislators, the Gadsden Purchase was scaled back from the original vision of President Pierce. This was an unusual circumstance where the United States could have obtained more territory but chose not to. Ultimately, Gadsden reached an agreement with Mexico to purchase about 30,000 square miles for $10 million. The treaty between the United States and Mexico was signed by James Gadsden on December 30, 1853, in Mexico City. And the treaty was ratified by the U.S. Senate in June 1854. The controversy over the Gadsden Purchase prevented the Pierce administration from adding any more territory to the United States. So the land acquired in 1854 essentially completed the 48 states of the mainland. Incidentally, the proposed southern rail route through the rough territory of the Gadsden Purchase was partly the inspiration for the U.S. Army to experiment by using camels. The secretary of war and proponent of the southern railway, Jefferson Davis, arranged for the military to obtain camels in the Middle East and ship them to Texas. It was believed the camels would eventually be used to map and explore the region of the newly acquired territory. Following the Gadsden Purchase, the powerful senator from Illinois, Stephen A. Douglas, wanted to organize territories through which a more northern railroad could run to the West Coast. And the political maneuvering of Douglas eventually led to the Kansas-Nebraska Act, which further intensified tensions over slavery. As for the railroad across the Southwest, that was not completed until 1883, nearly three decades after the Gadsden Purchase.